Normally bees seem very happy to share a flower with other bees or insects so I was surprised to see two bees fighting and watched them for over five minutes.   When I walked past later it seemed that one was dead.  I think they might be cuckoo bumble bees which can be aggressive towards normal bumble bees because they their eggs in their nests and leave the host bees to look after the larvae.  I would be interested if someone can enlighten me if they are indeed cuckoo bumble bees.